• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.21 no.1
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• pp.175-181
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• 2012

This paper presents a novel dynamic vibration absorber (DVA) to suppress the unbalance response of flexible rotor-bearing systems. The DVA unit consists of two DVAs, an adapter to place the DVAs and an adapter frame to locate the adapter. The essential feature of the proposed DVA unit is to place itself on any desirable location of the shaft without disassembling the rotor-bearing system under consideration. A simulation with a 3D element based commercial rotor dynamic software is made to test the possibility of the proposed DVA on the suppression of unbalance response in rotor-bearing systems. Experiments are performed to validate the proposed DVA unit. The simulation and experiments show that the proposed DVA unit is very effective to suppress the unbalance response in rotor-bearing system at designated rotational speeds of interest.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2001.05a
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• pp.811-818
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• 2001

ISO 11342 classifies flexible rotors in accordance with their balancing requirements and establishes methods of assessment of residual unbalance. This International Standard also shows how criteria for use in the balancing facility may be derived from either vibration limits specified for the assembled and installed machine or unbalance limits specified for the rotor. If such limits are not available, this standard shows how they may be derived from ISO 10816 and ISO 7919 if desired in terms of vibration, or from ISO 1940- 1 if desired in terms of permissible residual balance. This International Standard also presents methods for adapting the criteria of ISO 1940- 1 to flexible rotors.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.33 no.6
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• pp.92-99
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• 2005

Numerical analyses of critical speed and mass unbalance response are performed for a 30 ton thrust turbopump. The stiffness and damping of ball bearings and non-contact seals are quantified under aerodynamic and hydrodynamic loads induced by a fuel pump and turbine. Critical speed margin and tip displacements of the rotating parts are evaluated using a three-dimensional finite element method. The results are used to ensure the soundness of the rotordynamic design using an one-dimensional transfer matrix method. A further study shows that sufficient resonance margin may be assured via controlling the stiffness of the rotor support by employing an additional elastic ring to the bearing support.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1992.04a
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• pp.115-119
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• 1992

산업의 발전과 더불어 새로운 재료의 개발에 대한 요구가 날로 증가하고 있으며 이와 같은 요구에 부응하기위하여 각종의 신소재가 개발되고있다. 이들 신소재 중에서 섬유강화 복합재료는 높은 비탄성과 비강도특성 때문에 구조물의 경량화가 요구되는 우주선, 항공기 등에 주로 이용 되어 왔으며 최근에는 복합재료의 가격이 저렴해 지면서 이 재료의 높은 비탄성과 감쇠특성을 이용하고자 스포츠용품 및 기계 부품에도 섬유강화 복합재료의 이용이 증가 되고 있다. 항공기나 고속회전체의 부품을 복합재료로 제작하였을 경우 복합재료를 다른 금속이나 다른 복합재료부품에 접합(joining)시켜야 하는데 이 때문에구조물의 효율은 Joint에서 주로 죄우된다. Joint를 제작하기 위해서는 복합재료의 표면을 가공한 수 Adhesive를 이용하거나 Bolt로 체결하기 위해 구멍 뚫기 작업이 필요하여 드릴링을 하였을때 이 재료가 매우 연마성이 강하여 심한 공구마멸을 일으키며, 드릴의 입구와 출구쪽에서 각 ply들의 박리 현상이 발생하고, 드릴가공된 벽면으로부터 섬유 또는 레진의 탈락현상등이 발생하는 결점을 가지고 있다. 따라서 본 연구에서는 이러한 결점을 최소화하여 고정밀도의 높은 생산성을 얻기위한 가공기술에 대한 자료를 만들고 최적 절삭조건 및 복합재료가공용 드릴의 설계를 위한 지침을 제시하고자 고속도강 표준드릴을 사용하여 유리섬유 에폭시 복합재료및 탄소섬유 에폭시 복합재료의 드릴링 실험에서 절삭조건이 가공면 생성, 공구마멸, 절삭력에 미치는 영향에 대하여 조사하였다.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2001.05a
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• pp.695-701
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• 2001

While a rotating inner cylinder executes a periodic translational motion in concentric annulus, the vibration of the rotating inner cylinder is induced by fluid-dynamic forces acting on the cylinder. In the previous study related to journal bearing, the unsteady viscous flow in the annulus and the fluid-dynamic forces were evaluated based on a numerical approach. Considering the dynamic-characteristics of unsteady viscous flow, an approximate analytical method has been developed for estimating added mass, viscous damping and fluid-stiffness coefficients. For the study of flow-induced vibrations and related instabilities, it is of interest to separate the coefficients from the fluid-dynamic forces. The added-mass and viscous damping coefficients for very narrow annular configurations, as journal bearing. can be approximated by considering the gap ratio to the radius of inner cylinder, while the fluid-stiffness coefficient is related to the Reynolds number, the oscillatory Reynolds number and the gap ratio.